Manipulating The Magnetic Anisotropy Of Thin Films For3D Transition-metal And Their Alloys By Electric Field

Recently, manipulation of magnetocrystalline anisotropy （MCA） by external electricfield （EF） has attracted increasing attention, both for its fundamental interest and its hugepotential in magnetic recording technology. Increasing magnetic data storage density is themain goal for the hard-disk drive industry. To increase the storage density, the grain sizeneeds to be reduced. Therefore, materials with large perpendicular magnetic anisotropy arenecessary so as to overcome the thermal disturbance. However, as the same time,writability becomes a problem, since a higher magnetic field of the write head is required.Hence, the approach that allows MCA control by external EF is thus of great interest. Itoffered an alternative way to realize or assist the magnetization switching with ultra-lowenergy power consumptionIn order to get materials with a large EF effect, a variety of systems have been studiedboth theoretically and experimentally. It was found that the modification of MCA by EFcan be entirely different for different systems. An understanding of the underlying physicsbehind, however, is still lacking, thus hinders the further search of more promisingmaterials.In this paper, based on ab initio approach, we have investigated the mechanism of EFinduced MCA modification in metallic films. Start from a simple model of Fe, Co, Nimonolayer on a Cu（001） substrate, we found that the EF effect on MCA is very sensitiveto details of the Fermi level. To get a large MCA modification, the key factor is that theenergy bands cross of (d_xz and d_xy(or d_3z²-r²and d_yz) is close to the Fermi level.Moreover, the sign of the MCA slope with respect to EF can be well related to the fact thatthe cross point locates above or below the Fermi level.After that, the influence of heavy metal substrates （Rh, Pd） was consideredsystematically. For the Fe monolayer, using a Rh or Pd substrate instead of Cu willenhance the perpendicular magnetic anisotropy but weaken the EF effect. Finally, weextended our calculation to Fe_1-xCo_x alloy films on Rh（001） substrate, and found that it ispossible to get both large perpendicular magnetic anisotropy and a large EF effect bydoping with Co. In particular, the magnetization direction can be switched fromout-of-plane to in-plane by relatively small fields when the Co component x is about0.5,which could provide a wide possibility to design EF-driven spintronic devices.